ENTHALPIES OF FORMATION AND SOLUTION OF MACROCYCLIC AND NONCYCLIC TETRAAZA LIGANDS - ORIGINS OF THE ENTHALPY TERM IN THE MACROCYCLIC EFFECT

The heats of combustion of 1,4,8,11 -tetraazacyclotetradecane and 1,4,8,11 -tetraazaundecane have been determined by bomb calorimetry and the standard enthalpies of formation derived (-27.7±0.5 and -23.9±0.5 kcal mol-1, respectively). The enthalpies of solution of the same two compounds have been determined (-2.5 and -15.8 kcal mol-1, respectively) in 0.5 M NaOH. The gas-phase ΔHf° values of the ligands have been estimated and the macrocyclic enthalpy term, which has been determined previously for both Cu(II) (-4.7 kcal mol-1) and Ni(II) (-4.9 kcal mol-1) with these ligands, has been compared with the estimated difference in solvation energies of the two ligands (4.6 kcal mol-1). A general discussion on the terms contributing to the macrocyclic enthalpy is presented. © 1979, American Chemical Society. All rights reserved.